In recent years, in the retail industry, the checkout system using RFID (radio frequency identification) tags is often employed. This kind of system employs a tag reader. The tag reader reads data stored in RFID tags attached to products wirelessly, for example. Hereinafter, the data stored in RFID tags will be referred to as tag data. The tag reader reads the tag data, and the system therefore collects information on products that a buyer wants to buy.
If there is a plurality of RFID tags in the communication range of the tag reader, the plurality of RFID tags may send tag data simultaneously, the tag data may thereby interfere with each other, and the tag reader may not thereby read the tag data. The tag reader employs an anti-collision technology in order to prevent the situation, in which it is not possible to read tag data, from occurring. The tag reader, which employs the anti-collision technology, has an improved ability to reliably read tag data from all the RFID tags.
Some RFID tags are capable of storing data, which shows that a tag reader has read their tag data. Specifically, for example, a RFID tag stores a 1-bit flag, receives a predetermined command from a tag reader, and sets the flag. The RFID tag stores data, which shows that a tag reader has read its tag data, by setting the flag. The system is capable of confirming if the tag reader has read tag data or not by confirming the status of the flag of the RFID tag.
Further, in the past system, the tag reader sends a predetermined command if the tag reader reads tag data accurately. The predetermined command contains identification information of an RFID tag, which is contained in the tag data. Hereinafter, the identification information on an RFID tag will be referred to as tag code. The RFID tag receives the command. The RFID tag sets a flag if a tag code contained in the command is the same as its tag code.
Meanwhile, according to an idea of recent years, RFID tags are also used as security tags. For example, when a buyer brings products and passes through a security gate including the tag reader, the tag reader of the security gate reads tag data from RFID tags attached to the products. The security gate raises an alarm if a flag of the read tag data is not in the set-status.
As described above, when the tag reader reads tag data, RFID tags set the flags. If the tag reader reads tag data and then a buyer brings products, of which the payment processing is yet to be executed, and passes through the security gate, the security gate is not capable of detecting an abnormality.
In view of the above-mentioned circumstances, it is desirable to improve a function of preventing a buyer from bringing products out of a store unfairly in the past system, in which electronic tags such as RFID tags are used as security tags.